[MaterialButton] Add support for TOP & BOTTOM icon gravity

Is your feature request related to a problem? Please describe. Up until release 1.1.0-alpha06 back in May 2019, the only way to change the icon position was done using TextViewCompat.setCompoundDrawablesRelative.

After introducing new method setIconGravity in release 1.1.0-alpha06 it was finally possible to properly set the icon position, although only on the right or left, and close to the text or not.

This now excludes the possibility to place the icon either on top or bottom relative to the text.

Describe the solution you’d like Please kindly add TOP & BOTTOM gravity as part of @IconGravity.

Describe alternatives you’ve considered As said at the beginning, before release 1.1.0-alpha06, the only way to change the icon position was using TextViewCompat.setCompoundDrawablesRelative.

This no longer works, as it triggers a requestLayout which, at some point, will trigger updateIconPosition and then updateIcon where only START/TEXT & END/TEXT are supported.

[hrach]

Actually, in Gmail, there are buttons which have the icon on the left, but when insufficient width is there, they push the icon on the top. Seems pretty useful.

[rewgoes]

I’ve sent a PR adding top gravity only, let’s wait if it is approved!